About 40 city agencies have until midnight tonight to post their publicly available data to an online portal where anyone from citizens to government officials can access it.

It is the first milestone of the landmark open data law that was signed into law a year ago by Mayor Michael Blooomberg, and technologists, elected officials and advocates were celebrating the occasion.

"It's a baby step in the right direction, but it's a pretty big baby step," said Noel Hidalgo, executive director of the Open NY Forum and Code for America's local program manager. "You cannot reinvent the architecture and the practices of government within a year."

The much more significant data dump will take place over the next few years. By 2018, the agencies are expected to make available as much data public as possible under current law.

The Department of Information Technology and Telecommunications, which is helping agencies to unlock their data, says it expects a good number of agencies to comply.

Andrew Nicklin, Director of Research and Development at DoITT, said a handful of agencies — including the departments of Buildings and Housing Preservation and Development — faced hurdles in meeting the deadline because of Hurricane Sandy.

But he said that was understandable, given that "the city has a responsibility as much as possible to keep people sheltered." The law has built-in flexibility to allow agencies additional time if they can't meet the deadline.

Already there are hundreds of data sets available on the NYC OpenData portal — everything from restaurant inspection results to the city's favorite baby names. Though much of the information was largely available by going to each individual agency, it was often either in a format that made it impossible to analyze or was difficult to find.

At a celebration of the one-year mark of the law held at City Hall today, open government advocates said the data currently available on the OpenData portal was being used in a myriad of ways.

"We're seeing businesses use the open data, we're seeing advocates using it, we're seeing community boards using it," said John Kaehny, of Reinvent Albany, which co-chairs a group devoted to making city government more open and accountable. "This is pushing innovation, it's pushing open government, it's pushing transparency."

The next milestone, when agencies must provide a plan for putting online as much public data as possible, is in September.